1. Field of the Invention
The present invention relates to a drive apparatus for an optical recording medium such as an optical disk, more specifically relates to a drive apparatus for controlling spindle servo by switching it between fine servo by means of a fine servo loop and rough servo by means of a rough servo loop.
2. Description of the Related Art
In a recording/reproducing apparatus for recording and reproducing information onto/from a disk such as CD (Compact disk) or LD (laser disk), rotation of a spindle motor is controlled. This control includes two kinds of systems, i.e., fine servo and rough servo.
For example, in the fine servo on CD, a reproducing clock signal is extracted by a PLL circuit based on a EFM-modulated (Eight to Fourteen Modulation) RF signal, and the reproducing clock signal is compared with a reference clock signal so that a phase error signal and a speed error signal are generated, and driving of the spindle motor is controlled based on these error signals.
The rough servo is a system for extracting a synchronizing signal from an EFM-modulated RF signal and comparing the synchronizing signal with a reference clock signal so as to generate a speed error signal and to control driving of the spindle motor based on the speed error signal.
In a conventional reproducing apparatus for CD or the like, even during reproduction from CD or the like as well as at the time of starting the reproducing apparatus and at the time of a search operation, namely, even in the case where a reproducing clock is not extracted, the rotation is controlled accurately to a certain extent by switching between the fine servo and the rough servo.
However, according to the conventional system, since a ternary-controlled waveform, for example, is inputted directly into the spindle motor in the rough mode, the spindle motor is unnecessarily oscillated by its high frequency component, and thus resonance, which is peculiar to the spindle motor, is caused mainly due to axial resonance.
Since this resonance oscillates a disk mainly in a horizontal direction, the oscillation becomes disturbance, and a resonance waveform appears in the tracking error signal waveform. As a result, there is a problem that the stabilization of the tracking servo is prevented.
It is an object of the present invention to provide a drive apparatus for an optical recording medium which does not resonate a spindle motor at the time of rough servo.
A drive apparatus in accordance with the present invention is an apparatus for controlling a rotation of a motor for rotating a recording medium. The drive apparatus includes a fine servo control device for carrying out a fine control of the rotation of the motor using a reproduction clock, a rough servo control device for carrying out a rough control of the rotation of the motor using a frame synchronizing signal, and a selecting device for selecting one of the fine servo control device and the rough servo control device so as to carry out one of the fine control and rough control.
The fine servo control device includes: a fine servo signal generating device for generating a fine servo signal on the basis of the reproduction clock; and a first filtering device having a first frequency band for allowing first frequency components of the fine servo signal to pass therethrough;
The rough servo control device includes: a rough servo signal generating device for generating a rough servo signal on the basis of the frame synchronizing signal; and a second filtering device having a second frequency band for allowing second frequency components of the rough servo signal to pass therethrough. The upper limit of the second frequency band in the second filtering device is lower than that of the first frequency band in the first filtering device.
In the drive apparatus having such construction, when carrying out the fine servo control, the selecting device selects the fine servo control device. At this time, a reproduction clock is obtained from information recorded on the recording medium. The fine servo signal generating device then generates the fine servo signal on the basis of the reproduction clock. The first filtering device then extracts first frequency components from the fine servo signal. Then, the first frequency components are used for the fine servo control of the rotation of the motor.
The first frequency band in the first filtering device is set so as to extract the first frequency components from the fine servo signal. By extracting only the first frequency components from the fine servo signal, unnecessary high frequency components or noise components can be removed. Therefore, the accurate servo control can be achieved by the fine servo control device.
On the other hand, when carrying out the rough servo control, the selecting device selects the rough servo control. At this time, a frame synchronizing signal is obtained from information recorded on the recording medium. The rough servo signal generating device then generates the rough servo signal on the basis of the frame synchronizing signal. The second filtering device then extracts second frequency components from the rough servo signal. Then, the second frequency components are used for the rough servo control of the rotation of the motor.
The second frequency band in the second filtering device is set so as to extract the second frequency components from the second servo signal. By extracting only the second frequency components from the rough servo signal, unnecessary high frequency components or noise components can be removed. As a result, resonance of the motor due to high frequency components of the rough servo signal is reduced, and the stable servo control can be achieved by the rough servo control device.
Because the second frequency components used for the rough servo control is lower than the first frequency component used for the fine servo control in frequency, the upper limit of the second frequency band in the second filtering device is lower than the upper limit of the first frequency band in the first filtering device. Because the first frequency band and the second frequency band are independently set to the separate filtering devices, respectively, the filtering operation in the fine servo control device and the filtering operation in the rough servo control device are independent from each other. Even if the necessary frequency band for the fine servo control overlaps the unnecessary frequency band for the rough servo control, the necessary frequency component for the fine servo control can be extracted from the fine servo signal, and the unnecessary frequency component for the rough servo control can be removed from the rough servo signal.
As mentioned above, according to the present invention, in the fine servo control, the accurate servo operation can be realized, and the resonance of the motor is reduced in the rough servo control so that the satisfactory servo operation can be realized.
In case where a CD, a CD-R, a CD-R/W, a DVD, a DVD-RAM, a DVD-ROM or the like is used as the recording medium, it is preferable that the upper limit of the first frequency band is lower than 1000 Hz, and the upper limit of the second frequency band is lower than 500 Hz.
In the above-mentioned drive apparatus, the selecting device may select the fine servo control device at least when decoding information recorded on the recording medium so as to reproduce the decoded information, and the selecting device may select the rough servo control device at least when carrying out a search operation, a track jump operation or a starting operation of the apparatus. Thus, both the accurate reproduction of the decoded information and the stable search operation (the track jump operation or the starting operation) can be achieved.
In the above-mentioned drive apparatus, the fine servo control device may be provided as a loop circuit including the fine servo signal generating device and the first filtering device. Also, the rough servo control device may be provided as a loop circuit including the rough servo signal generating device and the second filtering device.
In the above-mentioned drive apparatus, the first filtering device may include a first low pass filter having a first cut-off frequency, and the second filtering device comprises a second low pass filter having a second cut-off frequency, and the second cut-off frequency is lower than the first cut-off frequency.
In the above-mentioned drive apparatus, the fine servo signal generating device may include: a first reference clock generating device for generating a first reference clock; and a first difference detecting device for detecting a difference in frequency between the reproduction clock and the first reference clock and generating the fine servo signal indicating the difference in frequency between the reproduction clock and the first reference clock. Furthermore, the rough servo signal generating device may include: a second reference clock generating device for generating a second reference clock; and a second difference detecting device for detecting a difference in frequency between the frame synchronizing signal and the second reference clock and generating the rough servo signal indicating the difference in frequency between the frame synchronizing signal and the second reference clock.